If folks are looking for an open source alternative to this, you should consider N1 and the Nylas sync engine.
With N1, you can run the entire stack yourself, or use our hosted version. Plus, N1 is built to be extended by developers using JavaScript, so you can build anything you want into it.
With N1, you can run the entire stack yourself, or use our hosted version. Plus, N1 is built to be extended by developers using JavaScript, so you can build anything you want into it.
More here: https://nylas.com/n1
(I work at Nylas.)